Vacuum brazing is normally carried out in a furnace connected to a vacuum pump and the brazing may typically take place at a temperature of about 1100.degree. C. and at a pressure of about 10.sup.-3 Torr. The low pressure is necessary to reduce the presence of molecular oxygen and gaseous oxygen-containing compounds to a minimum in view of the tendency of the metal parts being brazed to form oxide coatings. Oxide coatings which form on the metal surfaces to be joined and which remain at the brazing temperature seriously affect the wetting and flow properties of the brazing filler metal and thus the effectiveness of the brazing operation. The problem is particularly aggravated when the workpiece is formed from an alloy which contains an appreciable proportion of a particularly reactive metal, for example, a nickel or cobalt base high temperature alloy containing an aluminum and/or titanium addition to confer, for instance, age-hardening properties. There is a limit to the practical pressure reduction which can be achieved by a conventional vacuum pump, particularly because the effective pressure is that in the vicinity of the workpiece itself and this region, in which outgassing occurs, is baffled by the charge surround. A solution to this problem is to put in the furnace, at a point close to the workpiece for maximum effectiveness, a getter plate of a metal which has a greater affinity for oxygen than the workpiece. Titanium could be used for this purpose since substantially pure titanium or a high titanium content alloy would naturally be expected to have a greater affinity for oxygen than a titanium or aluminum alloy containing a relatively low proportion of titanium or aluminum (say 4-6%). However, titanium has not been found to be particularly effective and it has been necessary to use the more expensive metal zirconium. It has been found to be desirable to make the getter plate in the form of a shield, e.g., a cylinder with end plates, around the workpiece for maximum effectiveness. At the low pressures in question, this shield restricts admission of deleterious gases to the workpiece from the outside and performs a gettering function on gases which get into or arise within the enclosure.
A difficulty which has arisen in using this arrangement is that although the getter requires an elevated temperature to be effective, the brazing temperature is substantially higher than the optimum operating temperature for the getter and the getter tends to be mechanically weak and to sag at brazing temperatures. This can lead to serious damage to the workpiece and/or the support structure for the getter since zirconium and titanium, on the one hand, and iron, nickel, etc., on the other, fuse together to form low melting point phases at brazing temperatures. Thus, the use of titanium and zirconium getters is somewhat hazardous for use with very expensive workpieces.